[PATCH] ARM: vmlinux.lds: assert that ROM and RAM don't overlap when XIP_KERNEL=y

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Mon, Feb 01, 2016 at 06:02:34PM +0100, Ard Biesheuvel wrote:
> When building an XIP kernel, the linker produces two disjoint VMA regions,
> where the first is mapped onto ROM and the second onto RAM. For this reason,
> the linker output pointer '.' is updated halfway through the linker script,
> and set to a value that corresponds with the start of the RAM region.
> 
> However, in some cases, the ROM region exceeds the expected size, and the
> assignment of the output pointer results in a decrement rather than an
> increment, causing the virtual addresses of the .data region to clash with
> the .text region. Such a kernel cannot boot normally, but it also confuses
> the hell out of kallsyms, since .data symbols may appear inside the
> [_stext, _etext] or [_sinittext, _einittext] intervals in the first pass,
> but not in the second (or vice versa), resulting in inconsistent kallsyms
> data.
> 
> So let's make sure that the output pointer only advances, and never jumps
> back into the ROM region.

The long term goal is to move the XIP stuff out of this file, so
I think it's better to avoid touching this until the split has
happened.

I'd _much_ rather see the split happen first, and then fixes
applied, rather than trying to fix the existing unmaintainable
mess.

-- 
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